React useState hook is asynchronous!

Hello Developers 👋

I would like to share something I recently got to know, so the background is, in my project I was using useState value right after updating it and I was getting previous value(not updated value) and to my surprise I found out that useState hook is asynchronous

what it is?

Basically, the thing is you don't get update value right after updating state.

What is the work around/solution?

We can use the useEffect hook and add our state in the dependence array, and we will always get the updated value.

Show me the code 🤩🤩🤩

import { useState } from "react";

export default function CountWithoutEffect() {
    const [count, setCount] = useState(0);
    const [doubleCount, setDoubleCount] = useState(count * 2);
    const handleCount = () => {
        setCount(count + 1);
        setDoubleCount(count * 2); // This will not use the latest value of count
    };
    return (
        <div className="App">
            <div>
                <h2>Count Without useEffect</h2>
                <h3>Count: {count}</h3>
                <h3>Count * 2: {doubleCount}</h3>
                <button onClick={handleCount}>Count++</button>
            </div>
        </div>
    );
}

• Here we have very simple and stright forward component.
• On button click we are updating two states and one state is dependent on other state.
• The doubleCount will be one step behind count.
• Check out the Live Demo

Solving this issue 🧐🧐🧐

This can be easily solve with useEffect hook, let's see the code

import { useState, useEffect } from "react";

export default function CountWithEffect() {
    const [count, setCount] = useState(0);
    const [doubleCount, setDoubleCount] = useState(count * 2);
    const handleCount = () => {
        setCount(count + 1);
    };

    useEffect(() => {
        setDoubleCount(count * 2); // This will always use latest value of count
    }, [count]);

    return (
        <div>
            <h2>Count with useEffect</h2>
            <h3>Count: {count}</h3>
            <h3>Count * 2: {doubleCount}</h3>
            <button onClick={handleCount}>Count++</button>
        </div>
    );
}

• Here, when ever count changes we are updating doubleCount
• Check out the live Demo

Closing here 👋👋👋

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Comments

[Camillo Targas]

Very good, thank you!

[mahi kaushik]

"Great article! Understanding the asynchronous behavior of the useState hook in React is essential for writing efficient and effective code. While it can be easy to assume that the useState hook works synchronously like other functions, it's important to remember that React's state updates are batched and processed asynchronously for performance reasons.

The key takeaway from your article is that relying on the current value of state immediately after calling useState may not always return the most up-to-date value. Instead, you should use the callback function syntax to update state based on its previous value.

For those interested in learning more about React's useState hook, I recommend checking out this React usestate blog. Thanks for sharing your insights!"

[Froxx93]

In most cases you don't even need to make doubleCount a state.
You can simply say const doubleCount = count * 2; and it'll just calculate it new when count updates. Sometimes, when you have a more complex setup, useEffect might come in handy though.

[Manish]

Though in the above example it may not seem to make sense, but maybe we are rendering a component based on the doubleCount(or any state which is dependent on another), then just the variable doubleCount doesn't help in rendering the component as it changes

[Mohammed Nadeem Shareef]

Thanks for the info man... 😊

[Azeem]

Shareef Bacha

[abdullah565]

Thanks for this article.
But I wanna add here useState is not async. It is actually sync.

why it doesn't update immediately because of the closure.
more on this here: youtube.com/watch?v=RAJD4KpX8LA

thanks :)

PS: i'm still learning it how it does work and how react render works under the hood.

[Mohammed Nadeem Shareef]

Thanks for the input.

[Eliya]

Another (bit-tricky) way to solve this problem, is by setting the 'count' state with a callback, which returns an IIFE by itself, that will take the result of 'count' incremental as argument, sets doubleCount, and returns back the argument, which is the finally returned value for setCound.

[Rishi]

Another approach:- codesandbox.io/s/muddy-brook-iyzwk...

[Gabriel Pinheiro]

Can I use async/ await too?

[Mohammed Nadeem Shareef]

tbh
I don't know exactly may be you can or can't.
I would prefer not to use it.

[Simon Xiong]

Thanks for the writeup. Recently had to complete a project and ran into this issue. Now I at least know how to resolve it in future cases. 👍

[Mohammed Nadeem Shareef]

😄

[Diegoo11]

Muchas gracias, fue muy util.
Thank you very much, it was very useful.

[Mithun Varghese]

So recently I learnt this the hard way too. But what I realized is if you await setCount call, although it doesnot return a promise, the following code will execute after the count has incremented. Hope it helps :)

[Mohammed Nadeem Shareef]

Thanks for the info. I would love to read the hard way. It might help many of us.

[Lucila Gaudio]

I came to the same solution, I I think this is why: developer.mozilla.org/en-US/docs/W...